A fuel cell system disclosed in Tokkai H6-223855, published by the Japanese Patent Office in 1994, is known in the prior art.
This system comprises a fuel cell for generating electric power by causing hydrogen gas and oxygen gas to electrochemically react, a cooling water recirculation passage through which cooling water for adjusting the temperature of the fuel cell is recirculated, and a gas forcing device for removing the cooling water from the cooling water recirculation passage. When operations in the fuel cell system are shut down, the gas forcing device removes the cooling water in the cooling water recirculation passage and stores the cooling water in a container on the outside of the cooling water recirculation passage. The gas forcing device supplies oxygen or air from a gas supply source for supplying the fuel cell with gas to the cooling water recirculation passage through an open/close valve. In this manner the water to be circulated in the cooling water recirculation passage during operation of the fuel cell system is prevented from freezing after a shutdown of the fuel cell system in the prior art.